NCHRP 21-08 [Completed]
Assessment of Innovative Load Testing of Deep Foundations
| Project Data
||GTR--Geosciences Testing & Research, Inc.|
||Samuel G. Paikowsky|
||NCHRP Web-Only Document 84 Innovative Load Testing Systems|
Background: Performing static axial load tests on foundation elements is the most reliable method for determining allowable pile capacity and for obtaining information often needed to proceed with installation of production piles. However, conventional load testing is expensive and often time consuming, particularly when high-capacity foundations are involved. In recent years, several innovative methods have been developed that may offer technically viable, cost-effective alternatives to the conventional load testing of deep foundations.
These innovative methods have taken one of two forms: high-strain methods and expendable systems. High-strain methods for dynamic testing have been in existence since the late 1970s but have been used mainly during the installation of production piles. More recently, dynamic methods, including dropping heavy weights on foundation elements to measure deformations and ultimately estimate capacity, have been introduced. Another method, the STATNAMIC load test, is purported by its designer to be a rapid static load test with insignificant dynamic effects. Expendable systems such as the Osterberg load cell method and the SMARTPILE method have also shown some potential as a substitute for conventional load testing. Yet although these methods seem promising, technical issues related to both high-strain methods and expendable systems need to be addressed before definitive recommendations for their use as a substitute for conventional testing can be made.
Objective: The objectives of this research are to (1) recommend interim procedures for use and interpretation of innovative load testing methods for deep foundations and (2) develop a prioritized plan for the additional research, testing, and analysis needed to provide definitive guidelines for use of innovative load testing methods.
Tasks: Accomplishment of these objectives will involve at least the following tasks.
PHASE I: (1) Review and summarize pertinent domestic and foreign literature, ongoing research, and relevant practice related to innovative axial load testing methods. This review should include but not be limited to high-strain methods (e.g., drop weight and STATNAMIC) and expendable systems (e.g., Osterberg and SMARTPILE). (2) Critically assess each test method identified in Task 1, and evaluate related assumptions, practical and theoretical limitations, and empirical relationships used in interpreting test results. (3) Within 6 months after the effective date of the contract, submit an interim report that discusses and documents the information developed in Tasks 1 and 2. The interim report shall contain a revised work plan (as an appendix to the interim report) for Phase II and shall include an estimate of available data and data sources for each innovative load testing method discussed. Meet with the NCHRP project panel to discuss the interim report and the revised work plan. NCHRP approval of the interim report and of the revised work plan will be required before proceeding with Phase II.
PHASE II: (4) Collect and review data that compares innovative and conventional load tests for a range of subsurface, foundation, and loading conditions. The load-test reports, laboratory and field-test results, field notes, and other pertinent data from worldwide sources should be coded onto FHWA input forms. (5) The data from the hard copy forms compiled in Task 4 shall be remotely entered into the Deep Foundations Load Test Databases (DFLTD) using software supplied by FHWA. (6) Apply several broadly accepted methods of interpretation (e.g., Davisson's and DeBeer's) to the load displacement data from conventional and innovative load tests. Identify and analyze the mechanisms that lead to differences between the innovative and conventional test results. (7) Perform an assessment of the applicability, reliability, and cost-effectiveness of the innovative methods relative to conventional static load tests. (8) Based on the findings of Tasks 1 through 7, recommend interim procedures for use and interpretation of innovative load testing methods. (9) Submit a final report that documents the entire research effort. The final report shall include a prioritized plan for additional research, testing, and analysis needed to develop definitive guidelines for using innovative load testing methods.
Status: Research is complete.
Product Availability: The research agency's final report is available online as NCHRP Web-Only Document 84.